1. Field of the Invention
This invention is directed to wellbore casing cutting and retrieval tools and, in one aspect, to such tools used in retrieving wellheads in a marine environment.
2. Description of Related Art
It is known to cut and retrieve wellheads mounted on base plates and from which a casing string extends down into a wellbore, using a single-trip tool which combines a casing cutter and a grapple for releasably engaging the wellhead. Such systems are disclosed in U.S. Pat. No. 5,318,115, co-owned with the present invention and incorporated fully herein and in International Patent Application No. WO 91/02138.
There has long been a need for such systems in which movable locking arms are freely movable and not impeded by debris or cuttings. There has long been a need for such systems which are not inadvertently released from a wellhead.